Wildlife quickly returned to burned
areas after the 1988 fires in Yellowstone National Park.

Players lay black and white pebbles
on a gridded board, occasionally surrounding an unprotected line of their opponent's
markers -- prompting a victory swap to the engulfing color. After numerous reversals
of fortune, the tide turns and one will eventually engulf the other, triumphant.
This can take hours. Imagine every square on the board is an acre of forest. Black
pebbles are recent wildfires which completely burned the stand; white ones are
stands of healthy trees spared from flames by fire-suppression efforts. Surrounding
a fire keeps it from spreading, and eventually burned acres grow back to trees.
A square may switch between white and black several times.

"Go" in the
Real Woods

This game has played out for nearly a hundred years starting
in 1900. Lightning and periodic droughts made for a relatively constant number
of fires ignited, but the Forest Service's technology and political power to fight
fires increased. Slowly, the board turned white with fire-free foliage; only a
few pockets turned black each decade.

Today we are very nearly at what
looks like the end of the game, except that Nature has hidden the equivalent of
a doomsday device in that lovely blanket of white pebbles. The protected woods
have built up an enormous fuel load of downed and standing dead trees and limbs,
flammable underbrush and grass. With the right weather conditions -- high heat,
low humidity and heavy winds -- a single lightning strike or cigarette butt can
explode into mass fire that burns thousands of acres. The most valiant and well-equipped
firefighters are helpless when embers blow as much as a mile ahead of the main
fire, setting spot fires far beyond the widest fire lines.

Yellowstone's Inferno

This is what happened in 1988 when 1.5 million acres burned in the
Yellowstone National Park area. David Kovacic at the University of Illinois
Urbana-Champaign reconstructed the real-world "go" game of the park's
fire history by locating fire scars in tree cores. Any given stand used
to burn about once every 300 years, so the simulation begins in 1690
with the birth year of the oldest trees found inside the study area.
And instead of just white and black pebbles, Kovacic divided the "white,"
fire-free acres into four shades of green representing trees in different
age groups.

For almost 200 years, until about 1890, the pebbles of different-aged
trees jittered around as fire regularly burned some stands. Then fire-fighting
programs took hold and the entire forest progressively aged. By 1988 the mosaic
of high-fuel, fire-feeding areas and low-fuel, fire-stopping areas had become
homogeneous. The stage was set for the ensuing inferno -- and the flames spread
seamlessly through the woods.

Small Blazes Prevent Huge Ones

Kovacic's
reconstruction of Yellowstone's fire history yields two surprises. First, it turns
out the most important boundaries to wildfire are not geographical features like
roads, canyons or even rivers. Fire easily crossed them all. Rather, the boundaries
are biological. The crazy quilt produced by random fires turns out to be the forest's
best protection from fire.

The second surprise refutes the traditional ecological notion that stands
of old trees mark the end of the wilderness game of "go." Instead it's
the dancing cycle of growth -- life and death -- that is truly the steady
state. The ultimate paradox is that constant disturbance from fire on
a local scale maintains the stability of the larger ecosystem.